The present invention relates to drive control unit for an ultrasonic step motor, and more particularly to the drive circuitry for controlling the ultrasonic vibrations supplied to a step motor.
Conventional ultrasonic motors such as disclosed in Japanese Laid-Open Patent Publication Nos. 58-93477, 59-37673, 59-122385, and 60-51478, convert ultrasonic vibrational energy to rotational energy by applying a travelling wave to a set of vibrators to drive a rotor. The rotor rotates or otherwise continuously moves whenever and only when a driving voltage is applied to the stator of the motor. The motors operate inefficiently. Complex feedback control systems also must be provided and include circuitry for controlling the number of revolutions, stopping positions and/or rotational speed of the rotor. An undesirably high level in power consumption by the drive control unit results. Adjustment in the length of the step by the rotor also cannot be easily achieved. Undesirable manufacturing costs, additional assembly time and other related drawbacks also result.
It is therefore desirable to provide an ultrasonic motor which avoids such feedback control systems and, in particular, a step motor which operates more efficiently with drive circuitry which consumes less power and permits wide variation in the step movement of the rotor.